1. Field of the Invention
The present invention relates to a mirror holding device in a manuscript scanning apparatus adapted to guide a manuscript image through a mirror to an image receptor of a reading element, such as a surface of a photoreceptor or CCD and the like.
2. Description of the Prior Art
A so-called cantilever rod support type manuscript scanning apparatus has been known for use in optical system movement type copying machines and the like. In such manuscript scanning apparatus, a guide rail and a guide rod are spaced provided at a predetermined interval and extend in a scanning direction. First and second movable frame members each have at one end thereof a respective sliding member that is slidably supported on the guide rail. The opposite end side of each movable frame member is slidably engaged with the guide rod. The first movable frame is provided with an optical element comprising a light source for radiating a manuscript surface on a contact glass and a first mirror. The second movable frame member is provided with an optical element comprising second and third mirrors aligned at a second right angle for twice reflecting light reflected by the first mirror. A fixed fourth mirror is provided for reflecting a light reflected by the third mirror and then transmitting through an image forming lens unit toward the surface of the photoreceptor.
In such manuscript scanning apparatus, a first holding member holding one end of each mirror is provided with a first projection for supporting a mirror surface at one point midway in a direction of width thereof. A second holding member holding the opposite end of each mirror is provided with second and third projections for similarly supporting the mirror surface at two points in width direction thereof. First biasing means biases the mirror surface toward the first projection and second biasing means biases the mirror surface toward the second and third projections. Thus, the holding members support opposite ends of the mirror in a biased manner at a total of three points. However, all three points or projections act on the same surface of the mirror, and the direction of bias by the first biasing means is the same as that by the second biasing means. As a result, the problem occurs that the mirror is apt to be shifted in position by shocks caused by stopping and starting of driving of the optical system.
In addition, for example in the above described holding device for the fourth mirror, the mirror holding members for holding opposite longitudinal ends of the mirror are separately arranged so as to be changeable in posture around an axis parallel to an axis of rotation of the photoreceptor. This enables the position of a latent image on the surface of the photoreceptor to be regulated in a direction of rotation of the photoreceptor by changing the angle of reflection of the fourth mirror. However, it is remarkably difficult to separately change the posture of the mirror holding members without disturbing the balance of resolution of the image in a direction parallel to the axis of rotation of the photoreceptor. Also, the position of changing the reflecting angle of the fourth mirror is spaced from the mirror. Thus, a disadvantage has occurred in that the length of an optical path is changed substantially by regulation of the reflecting angle. Therefore, it is difficult to form the latent image on the surface of the photoreceptor at a predetermined magnification.
As shown in FIG. 11, in a conventional arrangement a movable frame member 62 has a sliding member 63 connected to member 62 by an eccentric cam 61, so that the height of sliding member 63 may be regulated up and down to correct a misaligned image due to error in parallelism of a mirror to a manuscript surface. The height from the sliding member 63 to movable frame member 62 is regulated by eccentric cam 61 in a case where the sliding member 63 becomes worn such that the mirror then is not parallel to the manuscript surface.
However, in such construction, upon loosening a screw member 64 in order to regulate the height, the movable frame member 62 will rotate around a guide rod 65 due to its own weight. Thus, during a height regulation operation, the height on the end of the movable frame member 62 must be held relative to guide rod 65 as a fulcrum, and screw member 64 must be tightened while maintaining such holding. However, it is almost impossible to fasten the screw member 64 while maintaining movable frame member 62 perfectly stationary at a precise regulated height. Thus, the operation of fastening or tightening the screw member 64 has been conducted as an approximation while taking into account up and down movement of the movable frame member 62 that inevitably occurs while attempting fastening of the screw member 64. However, it is no exaggeration to say that such manner of regulating the height is very rarely completed by one such operation, and thus disadvantages have occurred in that not only must such troublesome operation be repeated, but also precise regulation is remarkably difficult to achieve. In addition, since this manner of height regulation generally has been conducted by means of the cam and the like in the above described manner, the disadvantage exists that such separate regulating member must be added.